Cellular Mobile Telephone Systems Research Articles

Performance modeling of wireless networks with generally distributed handoff interarrival times

Handoff is an important issue in cellular mobile telephone systems. Recently, studies that question the validity of the assumption of handoff arrivals being Poissonian have appeared in the literature. The reasoning behind this claim can be summarized as follows: even if the new call arrival process is assumed to be Poisson, the handoff process due to dependencies with neighboring cells, call blocking and other reasons is not necessarily Poisson. The above-mentioned fact mandates the need to consider more general performance models that allow for arbitrarily distributed interarrival times. In this paper we provide numerical solutions for new and handoff call blocking probabilities with arbitrary handoff interarrival time distribution. For this purpose, we first prove that the underlying stochastic process is a Markov regenerative process and subsequently we use their mathematical theory to develop numerical techniques for important Quality of Service measures. Our results can be seen as a generalization of the recent work by Haring et al. [IEEE Trans. Vehi. Technol. 50 (2001) 664] where handoff traffic was assumed to form a Poisson process. Our work can be used for more accurate dimensioning of cellular systems with realistic traffic.

Objective Speech Quality Estimation for Analog Mobile Channels: Problems and Solutions

This article describes an objective speech quality assessment method developed for the Hungarian NMT-450 cellular mobile telephone system. The method is based on a psychoacoustic front end followed by a cognitive modeling component. Special problems of the NMT system, such as handover (HOV), the effects of automatic gain control (AGC), and the intrusion of signaling noise, are addressed in the cognitive module. Correlation between the subjective and objective quality measures is maximized by finding a transformation that linearizes their relationship. A correlation of 0.95 is achieved on an independent test set between the subjective speech quality and the proposed objective quality measure.

On the minimization of overhead in channel impulse response measurement

This paper presents a new method for channel impulse response measurement with a suitably designed binary sounding sequence. This method minimizes the system overhead and results in ideal channel estimation using three correlators instead of one. This system complexity can be easily overcome by the present technologies. The class of sounding sequences used in this method is the training sequence for channel impulse response measurement with the zero values of the autocorrelation function at all shifts except zero and middle shifts in European digital cellular mobile telephone systems based on the global system for mobile communication (GSM). Computer searches are carried out to find the suitable sounding sequences.

A cellular mobile telephone system with load sharing-an enhancement of directed retry

A load sharing facility, which enables subscribers in a mobile telephone system to look for free radio channels in more than one cell, is investigated with respect to blocking probability and channel utilization. Results show that a substantial improvement, compared to other channel allocation techniques, can be achieved. The positive effects are especially notable for an asymmetric traffic situation. The improvement is accomplished at the expense of an increased risk of cochannel interference between mobiles. >

Comparisons of channel-assignment strategies in cellular mobile telephone systems

Two novel channel-assignment strategies are proposed: the locally optimized dynamic assignment (LODA) strategy and the borrowing with directional channel-locking (BDCL) strategy. Their performance is compared with the fixed-assignment (FA) strategy (currently used on certain systems) and the borrowing with channel ordering (BCO) strategy (the strategy that has given the lowest blocking probability in previous research). Computer simulations on a 49-cell network for both uniform and nonuniform traffic showed that the average call-blocking probability of the BDCL strategy is always the lowest. The LODA performance is comparable with that of BCO under nonuniform traffic conditions but is inferior under uniform traffic conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Channel Utilization and Blocking Probability in a Cellular Mobile Telephone System with Directed Retry

A directed retry facility, which enables subscribers in a mobile telephone system to look for free radio channels in more than one cell, is investigated with respect to blocking probability and channel utilization. An iterative procedure is devised, by which the dependencies among cells can be illustrated. This procedure makes use of theories developed for overflow systems in classical telephony, and proves to be very accurate for the situations under study. Analytical results are compared with simulations and good agreement is observed. Results show that a substantial improvement, compared with systems without a directed retry facility, can be achieved as far as carried traffic is concerned. The improvement is accomplished at the expense of those subscribers who cannot make use of the directed retry facility due to variations in radio coverage.

Cellular Mobile Telephone Environment

Cellular mobile telephone systems are rapidly going into service throughout the Continental United States. They are being installed in a large variety of vehicles both of domestic and of foreign manufacture. In this paper we discuss the physical, climatic, and electronic environments which cellular telephones may expect to encounter in nationwide service. We also discuss procedures used to evaluate the ability of a cellular phone to operate without failure in these environments and to avoid interfering with the increasingly complex vehicular electronic systems.

UHF television interference associated with cellular mobile telephone systems

An investigation is made into two types of interference which may occur between UHF television and 850 MHz cellular mobile telephone systems: 1) ITV--interference to the cellular mobile telephone receivers, created by a UHF TV transmitter; 2) TVI--interference to the UHF TV receiver, created by the cellular system mobile transmitters. In the case of ITV it has been determined that TV transmitters operating on TV channels 65 through 69 may produce third-order intermodulation, within a radius of about 0.5 mi, to certain telephone channels assigned to mobiles operating in a cellular system fringe area. A judicious choice of telephone channel assignments would mitigate this type of degradation. Alternatively, in the case of TVI, it is shown that within a minimum grade B television service area, it is possible for cellular mobile telephones to at times produce image interference to present-day UHF TV receivers tuned to channels 58 through 61. However, because of cellular telephone subscriber density and channel position (and loading) the probability of interference is expected to be low. An increase of TV receiver image rejection by 20 dB would essentially eliminate all likelihood of this interference.

Throughput-delay characteristics and stability considerations of the access channel in a mobile telephone system

In this paper a performance study of the access channel in a cellular mobile telephone system /1/ is presented. The method used in the Cellular System for multiplexing the population of mobile terminals over the access channel is a hybrid between the methods known as CSMA/CD and BTMA. In the paper we extend an analysis of CSMA/CD to accomodate the function of the particular random multiaccess protocol. Results are shown which illustrate the equilibrium channel performance and the approximate stability-througput-delay tradeoff. Finally an estimate of the average message delay is given.

Satellite augmentation of cellular type mobile radio telephone systems

NASA's ATS-6 satellite relayed voice bandwidth communications between five trucks and the trucking company dispatchers as the trucks traveled throughout the north-eastern quarter of the contiguous United States. The experiment, conducted over a seven month period, demonstrated that propagation characteristics are much different for the satellite-mobile links than for terrestrial-mobile links. A properly designed satellite system can provide high quality, reliable voice and data communications except where the vehicle-satellite path is shadowed by a structure or terrain feature. Mobile equipment in the experiment was adapted from commercial mobile radios. The vehicle antennas were 75 cm tall, 2 cm diam. Another experiment proved the feasibility of vehicle position surveillance using active two-way tone-code ranging through ATS-6 to provide one line of position and passive one-way ranging by measuring the time-of-arrival of a signal from an independent satellite. A position fix was printed out at an earth station 1 sec after it sent the interrogation signal to the distant vehicle, a towboat on the Mississippi River. The line of position from ATS-6 was accurate to 0.1 nautical mile using a voice bandwidth ranging signal. The line of position from the NOAA GOES satellite was accurate to 2 miles, using 100 Hz signal bandwidth. If the signal from the independent satellite had the same bandwidth and signal-to-noise ratio as ATS-6, the fixes would have been accurate to about 0.1 nautical mile. A concept study concluded that satellites might be a cost effective augmentation of terrestrial cellular type mobile radio telephone systems. The satellites would serve thinly populated areas where terrestrial systems are not cost effective. In the United States, the satellites would serve about 90% of the land area where 20% of the population resides. A multibeam satellite with many channels in each beam would be compatible with the urban terrestrial systems and together they would provide a nearly ubiquitous mobile radio telephone service.

Data signaling functions for a cellular mobile telephone system

The Bell System is proposing to provide high capacity mobile telephone service in the 850-MHz band via a cellular system that employs frequency reuse within a geographic area. In this system, mobile units respond to orders received from base station sites, which are in turn controlled by data links from a telephone central office. Since all phases of the mobile telephone call, including call setup, handoff between base stations, and disconnect require extensive data signaling, a reliable data transmission facility must exist between the central office and the mobile units. The transmission facility consists of a land link and a radio link. The reliability of the radio transmission path is relatively low, and therefore error control techniques are necessarily more elaborate for the radio link than for the land link. Descriptions are given of the signaling requirements and of the signaling schemes devised for both the switching office-to-base station land path and base station-to-mobile unit radio path. The anticipated performance of the error control procedures for these paths is also presented.

Switching plan for a cellular mobile telephone system

Federal Communication Commission Docket 18 262 allocated a 75-MHz band to the common carriers to implement high capacity mobile telephone systems. The Bell System has proposed a cellular arrangement of low-power transmitters/receivers that permits frequency reuse in a coverage area. This method of achieving spectrum efficiency will require extensive centralized coordination and control to properly administer channel assignments and to interconnect the mobiles with each other and with the direct distance dialing (DDD) network. This can be accomplished by means of an electronic switching system (ESS) with special data terminals and trunking arrangements, and a unique program. In the proposed plan the radio sites (base stations) act effectively as remote concentrators in the frequency domain under the control of ESS, which in turn acts primarily as a trunk-to-trunk switcher. In addition to the usual switching, signaling, and supervising functions, the switching office must also perform numerous special functions including paging of mobiles, location of mobiles (signal strength and ranging data analysis), channel reassignment of mobiles, and reswitching of mobiles to various base stations-these last three occurring while customers ate talking.